Call blocking occurs when switching or transmission capacity in a network is not available at the time that a caller attempts to place a call. The lack of capacity that causes a call to be blocked may be located in many places in the network: the caller's own telephone switch, the caller's central office or in switches or transmission media in the long distance network. A blocked call may result in a caller receiving a “busy” signal, or in the call simply “hanging.”
The rate of call blocking in a network is a metric used in describing the grade of service of the network. Businesses often subscribe to communications services having a guaranteed maximum blocking rate, and are willing to pay for that enhancement. Communications network designers must therefore take into consideration a tradeoff between expense and grade of service. The expense of reducing blocked call rates typically increases at a greater rate as the number of blocked calls is reduced.
Telecommunications services providers have traced the occurrence of some blocked calls to the use of auto-dialers causing temporary congestion in the network. An auto-dialer is a device that attempts to establish telephone connections with each of a plurality of numbers in a list, or with a series of generated telephone numbers. Auto-dialers are typically used by telemarketers, public entities, etc. and are used in sending out or ‘call-blasting’ sometimes thousands of customers with pre-recorded messages for contests, surveys, emergency notifications, etc. The connection attempts are made in rapid succession, and may appear to the network to be effectively simultaneous. If the connection attempts are directed through a single network element such as a switch, the element capacity may be exceeded, resulting in the excess calls being blocked.
The problem of call blocking caused by auto-dialers is aggravated by the fact that disconnected numbers often remain on circulation databases longer than necessary. When auto-dialers attempt connections to a large number of discontinued telephone numbers, the intercept process consumes additional network resources and can itself result in additional blocked calls.
The use of auto-dialers and the occurrence of other mass calling events have resulted in increased blocking to be reported on various industry metrics and reports. Network operating companies are frequently rated on those metrics. The existence of those blocked calls may impair the ability of a company to guarantee that a dropped call rate will remain below a maximum number.
There has been a tremendous growth in the VoIP arena and a corresponding increase in call blocking of those calls. It is believed that the trunk groups handling VoIP calls have not been sized properly from the beginning.
In some computer networks, certain routers have an extra interface that automatically comes on when traffic gets too high on the primary interface. In telecommunications networks, an alternate route may be provided on switch or tandem equipment, serving a similar purpose. A problem inherent to that solution is that the alternate route can only handle so much traffic; thereafter, the alternate route begins to block traffic as well.
There is therefore a need for a technique and system for reducing call blocking in a telecommunications network.